Lifting jack



' Aug. 5, 1941.

H. scHyvERlN Filed July 11, 195B Patented Aug. 5, 1941 ea gr tries LIFTING JACK Frank H. Schwerin, Bellevue, Pa., assignor to The Duff-Norton Manufacturing Company, Pittsburgh, Pa., a corporation of Pennsylvania Application July 11, 1938, Serial No. 218,499

2 Claims.

This invention relates to lifting jacks in which the load-supporting top of the jack rests on a member which rotates during the raising and lowering of the jack. The simpler forms of screw jacks are of such construction, and this invention relates more particularly to screw jacks in which the top is connected directly to a screw which rotates in a stationary nut.

The outstanding merit of such jacks is their simplicity and corresponding low cost. The top on which the load rests should not rotate, but the screw does rotate and unless some means is provided for insuring low friction between the head and screw, the jack is difficult to operate because there is no mechanical advantage for overcoming such friction, except the leverage of the handle or bar by which the screw is rotated. This handle or bar fits directly into sockets in a capstan portion of the screw head, and it is therefore advantageous to keep the handle as short as possible so that it travels through a smaller sector in operating the jack.

It has been proposed to use ball-bearings to reduce the friction between the jack head and the raising and lowering screw. It is an object of this invention to provide an improved and simplified ball-bearing top construction for such jacks. The most notable advantage of the invention is that it provides a practical yet inexpensive construction that is in keeping with the simplicity of the jack as a whole.

It has been a difliculty of the prior art that much of the advantage of economical manufacture resulting from simplified design of risingscrew jacks was lost if the design were changed to incorporate ball-bearings between the top and screw. Ball-bearings require hardened raceways and in lifting jacks the bearings must be able to work under heavy loading.

Other features, objects and advantages of the invention will appear or be pointed out as the specification proceeds.

The drawing shows a sectional View of the preferred embodiment of the invention.

The jack has a frame H] which flares out at its lower end into a bell base H. The upper end portion I2 has a threaded interior which comprises the nut for a screw M. On one side of the frame It there is a handle it which is preferably cast integral with the frame.

A screw head H5 at the upper end of the screw is integral with the screw and has two intersecting passages l1 and I8 extending at right angles to one another and serving as sockets into which a handle is inserted to turn the screw to raise or lower the jack.

The jack has a cap or top 20 with a hole 2| through which extends a reduced end portion or stud 22- of the screw head. The stud 22 is preferably integral with a capstan portion of the screw head below it. The diameter of the end 22 where it extends through the hole 2! is slightly less than the diameter of the hole, to make the top 29 a free fit on the end 22 of the screw head. The upper extremity of the end 22 is peened over to form a flaring head 24 that prevents the top 20 from being lifted off the screw head, but the flaring head 24 does not prevent the top 20 from rotating freely with respect to the screw It. A recess in the upper face of the top 20 prevents the flaring head 24 from coming into contact with the load that is lifted by the jack.

A washer 25 rests on the upper annular face of the large diameter or capstan portion of the screw head It. The upper face of the washer is hardened, and when the jack is manufactured this hardened face is plane and preferably normal to the cylindrical surface of the end portion 22. The washer 25 serves as the lower raceway for balls 26.

The lower side of the top 2t has a recess 28 slightly larger than the capstan portion of the screw head IS. The lower part of the top 2|] forms a skirt that has ample clearance from the screw head !6 to permit free relative rotation of the top 29 and screw head 16, but this skirt serves as a shield to keep dirt and other foreign matter from getting into the annular space in which the balls 26 are housed.

In machining the recess 28 a portion of it is made with a diameter just a little larger than the diameter of the end portion 22 plus twice the diameter of a ball 26 so that the balls are confined against lateral displacement by the wall of the recess. There is a washer 29 at the end of the recess 28 above the balls. The lower face of the washer 29 is hardened, and this hardened face is preferably plane when the jack is manufactured.

The full circle of balls 26 confined between the washers 25 and 29 have only point contact with these washers as long as the surfacehardened faces of the washers are plane. When the jack is used under load, the balls 26 roll themselves a shallow groove in each of the washers. This is possible because the washers have a soft core and the metal behind the faces is displaced when the hardened faces bend under pressure. Experience shows, however, that after the grooves reach a certain depth the unit loading of the balls on the washer faces is so reduced that the depth of the grooves does not increase any further and the grooves serve as effective rac-eways for the balls.

It will be apparent that the construction described provides a ball-bearing top which is simple and inexpensive and which will take angular thrusts from all directions. Changes and modifications, however, can be made in the construction illustrated without departing from the invention defined in the claims.

I claim:

1. In a rising-screw lifting jack of the class wherein a rotatable screw threads through a frame and has a head comprising a capstan portion with a stud of smaller diameter than the capstan portion extending upward from said capstan portion, and a load-supporting top surrounds the stud and is rotatable with respect to said stud, and the top has a recess in its bottom face that forms with the upper surface of said capstan portion an annular chamber for ball-bearings, the combination with the screw head and load-supporting top of balls located within said annular chamber, said balls being of a diameter substantially equal to the width of said annular chamber, a washer in the recess above the balls, and a lower washer located beneath the balls and supported by the upper surface of the capstan portion of the head, each of said washers having a soft core and having a hardened face in contact with the balls, and the recess in the load-supporting top being sufficiently deep so that said top extends down beyond the hardened face of the lower washer and encloses the ball-containing chamber.

2. In a rising-screw lifting jack of the class wherein a rotatable screw threads through a frame and a load-supporting top is rotatable with respect to the screw and has an opening into which an upper end portion of the screw extends, and a capstan portion of the screw is of larger diameter than said upper end portion and cooperates with a recess in the lower side of said top to form an annular chamber for a ball-bearing, the side of said recess extending down toward the capstan portion of the scre v and forming a skirt for excluding dirt from the annular chamber, the combination with said capstan portion of the screw and loadsupporting top of balls located within the annular chamber, an upper washer in said recess above the balls, and a lower washer located below the balls and resting on the upper surface of the capstan portion of the screw, both of saidwashers having hardened faces in contact with the ball.

FRANK H. SCHWERIN. 

